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How do I paint on an RGBA texture's alpha channel in Blender 2.73?

I'm not actually using it for transparency, so I would prefer to visualize the alpha channel as a grayscale image while painting, if that's possible.

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The paint modes named Add Alpha and Erase Alpha may be what you are looking for.

enter image description here

If you are using a pen tablet then you can use the pen eraser to use Erase Alpha without having to change the blend mode in the UI. There does not yet seem to be an alt key press that allows the pen eraser to toggle between Erase and Add.

Personally, I think the better way, for now, is to paint the texture the usual way and then use GIMP to add this texture to the Alpha channel of some other texture. Blender does not really seem streamlined yet for working with and packing multiple images together in a convenient way. Maybe I'm just missing something and it's all there nicely workable already, blender can do lots of things that are not well documented :)

If you follow this link, I show how to add an image to the alpha channel of another image using GIMP. Dotted line on curve?

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  • $\begingroup$ Yeah, I might end up doing it outside of Blender, but I'll try Add/Erase Alpha for now. Followup question: is there a way to change the color to something other than white when alpha is 0? (Black would be more natural, at least for what I'm doing.) $\endgroup$ – KTC May 11 '15 at 18:25
  • $\begingroup$ I don't use this ability so I'm only mostly guessing but I think the 'white' is the Viewport Material color. The Black is the default texture color. If you look in the left window shown above, you can see that there is no white. It's transparent. You could put another texture on the lower slot that can be any color you want. $\endgroup$ – MarcClintDion May 12 '15 at 4:26

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